The Iris Robinson affair took on a new dimension in Belfast last night when it was announced that Northern Ireland police are launching an inquiry into her tangled financial dealings.

Police said their organised crime branch had been called in to establish whether any criminal offence had been committed. The move follows revelations concerning both Mrs Robinson's sexual behaviour and her financial arrangements. It has been reported that she obtained £50,000 from two building developers to help her teenage lover, Kirk McCambley, in his business.

In recent weeks Mrs Robinson has stood down as an MP, resigned from other offices and been expelled from the Democratic Unionist party, which is headed by her husband Peter.

Her husband, who is Northern Ireland's First Minister, has mounted a robust defence of his role in the episode, maintaining that he has done nothing wrong. But there has been no such defence on behalf of Mrs Robinson, whose comments have been limited to one brief statement after the news of her affair emerged.

Medical authorities have confirmed that she is receiving acute psychiatric care, while her husband has said that she is unable to give coherent replies to questions.

The cheques for her lover helped him gain a contract to run a café on behalf of Castlereagh district council, of which she was a member. She voted in favour of his bid but did not declare an interest in the project as required.

The council has already set up an inquiry to examine how the contract was handed out and Westminster and the Belfast Assembly are to examine the question of whether codes of conduct were committed.